A large number of people suffer from health conditions which are either directly or indirectly related to their cardiac function. For example, hypertension refers to a chronic disease in which the patient's systemic blood pressure is elevated above that which is considered a healthy level. As a chronic condition, hypertension can contribute to a wide variety of well-known health ailments. Accordingly, therapy for a known hypertension condition is typically prescribed to ameliorate the hypertension condition and related effects. Depending on the severity of the hypertension as well as the patient's individual condition, typical therapies can include diet modification, an exercise regimen, and/or a medication regimen.
Another category of cardiac related health ailments include cardiac arrhythmias. A number of medications are known which can help restore, at least partially, more normal sinus rhythm for certain patients. Another known category of therapy for cardiac arrhythmias includes implantable cardiac stimulation devices, such as pacemakers and/or implantable cardioverter-defibrillators (ICDs). Implantable cardiac stimulation devices automatically monitor the ongoing cardiac activity of the patient and selectively provide direct electrical stimulation to the cardiac tissue when indicated in an attempt to restore the patient's intrinsic rhythm to a sinus rhythm or alternatively to substitute for the patient's intrinsic rhythm and assume control of the heart's activity for at least some period of time, such as in pacing.
One particular health ailment that frequently can be effectively treated with an implantable cardiac stimulation device is paroxysmal atrial fibrillation (AF). AF is a condition of rapid, chaotic atrial contractions that results in much less effective atrial pumping and reduced overall cardiac efficiency. Paroxysmal refers to sudden periodic recurrence or worsening of the AF. AF is not generally life-threatening, however occurrences of AF frequently contribute to further ongoing episodes of AF. AF is also known to increase the risk of thromboembolism and has been associated with heart failure (HF).
An implantable cardiac stimulation device can be provided and programmed to deliver atrial overdrive pacing as therapy for paroxysmal AF. The device is typically programmed to provide atrial pacing stimulation at a rate generally 5-20 pulses per minute (ppm) greater than an intrinsic rate. This atrial overdrive suppresses recurrence of AF episodes. A drawback to this therapy however is that the artificially elevated heart rate induced by the atrial overdrive pacing is irritating to some patients and can disrupt restful sleep.
One possible alternative to providing therapy while avoiding the physiologic drawbacks of overdrive pacing would be to provide some manner of indirect therapy or stimulation, such as provided by the body's natural feedback mechanisms. For example, providing stimulation to the vagus and/or sympathetic nerves has been considered as a possible avenue for therapy delivery. However, it has as yet proven impractical to access these nerves and to realize effective placement of leads on them to provide stimulation on a long-term basis.
Thus, it will be understood that there is an ongoing need for providing interventional therapy in a manner which reduces the negative consequences or side effects of known therapies. There is also a desire for therapy which is relatively inexpensive and simple to implement and also for therapy which more closely emulates natural physiological feedback and response.